A Timaru raw milk provider will keep its doors shut until at least the end of the week after subsequent tests for campylobacter proved positive.

Village Milk Timaru shut their doors last week after Community and Public Health confirmed seven cases of people contracting campylobacter were linked to milk purchased from the business on March 7 and 8.

Franchise owners Stu and Andrea Weir hoped to reopen by the end of the week, but confirmed this might not happen.

''There is more testing to be done. We don't know precisely what the cause of the original outbreak was. It could be from one of the introduced cows, or it could be part of the water supply was contaminated. We have to canvass every possible option,'' Stu Weir said.

Village Milk chief executive Mark Houston posted on the company's Facebook page, saying the presumptive milk test results for last week's samples were still positive for campylobacter.

''We are now widening the search for a cause and have sent water samples away for analysis. We will not be able to reopen until we have a clear understanding of the cause of this problem and a solution that we can rely on to make sure the milk is safe to drink,'' Houston said.

Stu Weir said the problem was only related to the raw milk supply.

The Ministry for Primary Industries has also launched an investigation.

''Any time there is an illness linked to a food source any leftover food can be sent for testing by the investigating officer,'' a spokesman said.

''In the case of raw milk, the product in question has almost always been consumed by the time people get sick, so there is nothing for investigators to test.''

The spokesman said the MPI had not confirmed the source of the contamination.